The use of electrodes to sense and measure bio-potential signals is widely practiced in the medical field as part of the various diagnostic tools such as electrocardiography (ECG/EKG) for monitoring heart function, electromyography (EMG) for monitoring muscle activity and electroencephalography (EEG) for studying brain activity and the like. The prior art for these techniques is to use a metal electrode which is in contact with its ionic form through a gel-bound electrolyte which then contacts the skin. A commonly used system of this type is the “wet” electrode which is typically an Ag/AgCl electrode. These systems suffer from many disadvantages documented in literature such as the requirement of skin preparation including removal of hairs by shaving, and removal of the stratum corneum by scrubbing. Furthermore, wet electrodes commonly cause skin irritation in persons with sensitive skin.
Licata and Mitchell disclosed the use of soft elastomeric bristles filled with a conductive liquid as a biopotential sensor (see U.S. Pat. No. 6,510,333). The technique of U.S. Pat. No. 6,510,333 does not require preparation of the skin, however it does require liquid to be in the bristles and also recommends an abrasive scrubbing of the skin in order to eliminate resistance from the surface of the skin. The bristles also require refilling throughout their lifetime which can be an added inconvenience to the user.
Schmidt, Lisy, Skebe, and Prince from Orbital Research Inc. (U.S. Pat. No. 7,032,301) disclosed a dry physiological recording electrode that does not require any skin preparation. This assembly requires constant contact with the skin. To ensure constant contact the assembly pierces the skin in order to obtain a biopotential signal which can cause pain and discomfort to the user.
Lin and Liao (see U.S. Pat. Pub. No. 2014/0058243) disclosed a dry electrode device and fabrication methods. However, their electrode uses multiple spring loaded pogo pins, and the metal probes cause discomfort to user and can scratch the head. Additionally, monitoring a moving subject is a challenge as the spring probes move up and down and the skin-electrode impedance changes, which causes noise in the signal.
Chi from Cognionics Inc (see U.S. Pat. Pub. Nos. 2013/0102874 and 2013/0066185) disclosed a dry electrode with a mechanism for noise reduction on a moving subject. However, their dry flex electrode can experience several issues, such as a lack of bandwidth, higher electrode impedance (50-300 kohm) than the accepted standard range for medical EEG recording (less than 5 kohm) and no MRI compatibility.